A seizure is an overexcitable state of nerve cells in
the brain, sometimes leading to sudden, violent,
involuntary contractions of a group of muscles
and/or manifestations of decreased awareness of
environmental surroundings (e.g., blank stare with
A contraction is shortening and thickening of the
muscles. Seizures can occur in distinct predictable
episodes (as in a chronic seizure disorder)
independent of external events or they can occur
suddenly in response to an external event such as a
traumatic brain injury.
During a seizure, nerve cells
(gray) fire electric impulses too
rapidly and frequently (red).
Seizures are sometimes described as focal, which means that they originate from a
specific region of the brain. Seizures are sometimes described as unilateral or bilateral,
meaning that they can originate from one or both sides of the brain, respectively.
Seizures are sometimes described as partial, which also means that they come from one
area of the brain.
If seizures are described as generalized, this means that the disruption of nerve cells
spread from one brain region to multiple brain regions on both sides. Some seizures are
described as tonic, meaning that the muscles (usually the limbs) are extended and stiff.
Others seizures are described as clonic, meaning
that the muscles are jerking back and forth. When
tonic and clonic seizures occur together they are
known as tonic-clonic seizures.
The word "seizure" is sometimes use as a general
term to describe an attack, the sudden onset of a
disease, or the sudden onset of certain
symptoms. Recurrent episodes of seizures are
typically referred to as epilepsy. A seizure is also
known as a convulsion. Seizure comes from the
Old French word "seisir" meaning "to grasp."